The storm, which currently covers about 7 million square miles (18 million square kilometers) of the red planet, is blocking sunlight form reaching the solar-powered rovers' light-collecting arrays (see a Mars map).

As the power supply dwindles, NASA scientists are sending commands to shut off the rovers during noncritical hours.

"We only plan to stay up for a short period of time, and then we command the vehicle to go to sleep," said Jacob Matijevic, chief of the rover engineering team, who is based at NASA's Jet Propulsion Laboratory in California.

"Fortunately this [storm] came at a time when it's the summer season in the south of Mars, so we don't need the energy for survival heat."

During southern winter, when temperatures can plummet as low as -125°F (-87°C), a loss of self-generated heat would expose the rover to surface temperatures that would likely cause extensive damage.

Although some experts worry that the continuing storm will eventually drain the rovers and cause a final powering down, Matijevic is confident that the storm will soon pass.

"It's a low-activity period," he told National Geographic News, "but we're not in a position that threatens our survival."